The instant invention concerns the removal of hydrocarbon values from drill cuttings which have been contaminated with hydrocarbons.
During rotary drilling operations, a volume of the subterraneous material encountered is removed to provide the well bore. This material is generally referred to as drill cuttings. The cuttings are usually mixed with the drilling fluid used and any water or hydrocarbons encountered subterraneously during drilling operations.
In a typical drilling operation, the cuttings are separated from the drilling fluid by way of a shale shaker. The recovered drilling fluid is usually recirculated for further use in the drilling operation. The cuttings removed by the shale shaker are not only coated with but contain a mixture of water, hydrocarbons and constituents of the drilling fluid. In some cases, the drilling fluid itself may contain hydrocarbons which contribute to the contamination of drill cuttings.
When the drilling operation takes place onshore, the disposal of cuttings does not generally present a difficulty. Often times the cuttings are used as landfill. When drilling operations are undertaken offshore, the disposal of cuttings presents a substantial problem. If the cuttings are simply dumped into the water, a serious pollution problem may be created and the dumping of oil containing cuttings appears to be illegal. The U.S. Department of the Interior in OCS Orders 1-12 has ordered that drill cuttings shall not be dumped into the ocean unless the oil has been removed. Several methods and apparatus have been disclosed for cleaning hydrocarbon contaminated cuttings.
U.S. Pat. No. 3,693,951 discloses a method and apparatus for treating well cuttings which includes a high intensity infrared heating chamber. In this process, the hydrocarbons are combusted.
Chemical processes for treating drill cuttings have been proposed. For example, U.S. Pat. No. 3,860,019 and 3,693,733 disclose a method and apparatus for washing drill cuttings by use of a detergent circulatory system. In addition to the chemical treatment disclosed in those patents, other chemical processes are known. For example, the Brant Company presently commercializes a drill cuttings unit which employs a chemical process to clean drill cuttings.
Other methods of cleaning drill cuttings have been proposed or used. For example, cuttings have been placed in a high temperature retort and heated to a temperature sufficient to combust the hydrocarbons contaminating the cuttings. This process is not practical because of the materials handling problem created and because of the high level of energy required to combust the hydrocarbons.
While several methods for cleaning hydrocarbon contaminated drill cuttings are known, these methods have their disadvantages. For example, in those methods which require chemical treatment, storage and disposal of the chemicals would appear to be a problem. Also, chemical treatments do not fully remove all hydrocarbons from the cuttings and in some cases the chemicals may be more damaging to the environment than the hydrocarbon they remove. Some of the methods would appear to be economically unsound because of the high energy requirement. Other methods would appear to be impractical for use in treating drill cuttings offshore because the equipment required can not be contained in a compact unit. Moreover, none of the methods disclose a relatively simple manner of removing and recovering substantially all hydrocarbon values from the contaminated material and producing a clean material having negligible quantities of hydrocarbons.
It would therefore be advantageous to provide an apparatus and method for cleaning oil contaminated drill cuttings which is energy efficient, does not require the addition of chemicals, is relatively compact, removes substantially all of the hydrocarbons contaminating the cuttings and provides for the recovery of the hydrocarbons values removed from the contaminated material.